<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>背景框</title>
  <style>
    .envelope {
      width: 300px;
      height: 100px;
      border: 20px solid transparent;
      background: linear-gradient(white, white) padding-box,
      repeating-linear-gradient(-45deg, red 0, red 20px, white 0, white 40px, cornflowerblue 0, cornflowerblue 60px, white 0, white 80px) border-box;
    }

    @keyframes ant-move {
      to {
        background-position: 100% 100%
      }
    }

    .ant-border {
      width: 300px;
      height: 100px;
      padding: 1em;
      border: 1px solid transparent;
      background: linear-gradient(white, white) padding-box,
      repeating-linear-gradient(-45deg, black 0, black 25%, transparent 0, transparent 50%);
      background-size: 100% 100%,.6em .6em;
      animation: ant-move 12s linear infinite;
    }
  </style>
</head>
<body>
<div class="envelope">
  This is a letter from Samuel to ZhangBoy, ZhangBoy is a beautiful and interesting girl.Samuel really really love her.
</div>
<div class="ant-border"></div>
</body>
</html>